High temperature nickel base alloys



United States Patent 3,393,999 HIGH TEMPERATURE NICKEL BASE ALLOYS Louis W. Lherbier, Cuddy, and Norman R. Harpster, Titusville, Pa., assignors to Cyclops Corporation, Bridgeville, Pa., a corporation of Pennsylvania No Drawing. Filed Dec. 27, 1965, Ser. No. 516,695 5 Claims. (Cl. 75--171) ABSTRACT OF THE DISCLOSURE A high temperature nickel base, chrome, tungsten, and cobalt alloy characterized by good high temperature strength, good thermal stability, good resistance to corrosion, oxidation and wear, and satisfactory workability and machineability.

The present invention relates to nickel base alloys and, more particularly to alloys especially adapted for use in the manufacture of internal combustion engine parts, turbine parts, such as blades and wheels, and parts of jet engines, because of the unique properties possessed by parts made therefrom.

Alloys for use in the above applications must have good mechanical strength at high temperatures as well as long duration thermal stability. Additionally, the alloys must have good resistance to wear, corrosion and oxidation since the parts made therefrom are subject to continuous use and to exposure to high temperature combustion gases. The alloys must also be capable of hot fabrication and must be easily machineable. The use of presently existing alloys in this field has been limited by the inability of the alloys to fulfill all of the above requirements. Many alloys which exhibit good mechanical properties at high temperatures cannot be exposed to corrosive or oxidizing atmospheres at high temperatures, while other alloys which are capable of withstanding corrosion and oxidation at high temperatures do not possess the necessary strength and thermal stability.

In an attempt to overcome the defects of the known alloys and obtain engine parts having all of the properties necessary to enable use at high temperature engine conditions, composite parts have been made with a core of one material and a coating of a dilferent material. For example, valves have been made with a core of an alloy having good high temperature strength and thermal stability and a coating of an alloy having good corrosion, oxidation and wear resistance. A composite part made in this manner is both expensive and difiicult to manufacture and still does not exhibit the desired high temperature strength and stability.

We have found that the desirable attributes indicated above, namely, good high temperature strength and stability, resistance to corrosion, oxidation and wear, hot fabricability and machineability can be obtained in a nickel base alloy by maintaining the various elements within certain ranges. Due to the properties of our alloy, it is especially suited for the manufacture of parts subject to high temperature under conditions such as are encountered in combustion engines and turbines. Additionally, the alloys of our invention are relatively inexpensive to produce since they do not contain a large amount of expensive alloying elements and can be made by well-known melting practices.

The alloys of our invention possessing the properties indicated above fall within the following composition ranges:

Percent Carbon 0.20-0.60 Manganese 0.30 max. Silicon 0.35 max. Chromium 22.5-24.5 Tungsten 5.0-8.0 Cobalt 5.0-12.0 Iron 3.0 max. Nickel 50.0-65.0

Elements such as sulfur, phosphorus, aluminum, etc. may be present in trace amounts resulting from normal melting practice.

While the composition ranges specified above will provide alloys havin-g the above-mentioned properties, a preferred composition range is as follows:

Percent Carbon 0.35-0.45 Manganese 0.30 max. Silicon 0.35 max. Chromium 22.5-24.5 Tungsten 6.0-8.0 Cobalt 8.0-1025 Iron 3.0 max. Nickel 50.0-60.0

A typical alloy having all of the properties required for use in high temperature engine parts. is as follows:

Percent Carbon 0.40 Manganese 0.20 Silicon 0.20 Chr mium 24.0 Tungsten 7.0 Cobalt 10.0 Iron 2.0 max. Nickel Balance In respect of the various alloying elements used in our composition, we have determined that a carbon range of 0.20 to 0.60 percent is required. An alloy containing less than 0.20 percent carbon does not have the neces sary strength at high temperatures and is not sufficiently wear resistant for use in engine parts, while an alloy containing more than 0.60 percent carbon cannot be successfully hot worked. It has also been determined that no nitrogen should be added to our composition since the hot strength of the alloy is not materially increased thereby and the hot workability is adversely atfected.

The manganese content has been expressly set at 0.30 percent maximum since manganese in excess of 0.30 percent permits the formation of spinel-forrning surface oxides which impair oxidation and corrosion resistance at high temperature. Although manganese enhances the hot workability of the alloy to a certain extent, it is not essential. Silicon is used as a deoxidizer during the melting of the alloy but must not exceed 0.35 percent since it adversely affects hot workability.

Chromium has a desirable effect on corrosion and oxidation resistance and our alloy must have a minimum of 22.5 percent chromium in order to have sufficient corrosion resistance and oxidation resistance. However, the chromium content of our alloy should not exceed 24.5 percent since chromium in excess of this amount makes the alloy extremely difficult to hot work. Additionally, tests have shown that a chromium content over 24.5 percent adversely affects the creep strength of our alloy.

Tungsten is added to our alloy to enhance the strength of the austenitic matrix afforded by the high nickel content and it thereby provides the alloy with the necessary strength at high temperatures and with good wear resistance. The minimum tungsten content which will provide the alloy with the necessary high temperature strength is 5.0 percent. Although increasing amounts of tungsten increase the hot strength of the alloy, we have determined that over 8.0 percent tungsten creates oxidation problems and decreases the hot workability. Additionally, we have found that tungsten can be added to the alloy without the drawbacks associated with molybdenum, titanium, aluminum, columbium and tantalum.

Cobalt is, of course, added to our alloy to enhance the high temperature strength and ductility of the alloy, and the presence of cobalt in our high temperature nickel base alloy increases the life of a part made of the alloy and significantly lowers the creep rate of the material. The lower limit of the cobalt content is dictated by the properties required and We have determined that 5.0 percent is the minimum amount of cobalt which can be used if the alloy is to have the required strength and creep rate. Cobalt in excess of the upper limit of 12.0 percent tends to create corrosion problems in the alloy. It is also desired to maintain the cobalt content at 12.0 percent or lower to keep the cost of the alloy at a minimum.

It is essential that the iron content of the alloy not exceed 3.0 percent since over 3.0 percent iron adversely affects the corrosion resistance of the alloy. Actually the iron content of the alloy results from the melting procedure used to manufacture the alloy and should preferably be kept at a minimum or eliminated altogether even though up to 3.0 percent can be tolerated.

A minimum nickel content of 50 percent is necessary in our alloy to insure a single phase structure at the elevated temperatures for which the alloy is designed. The maximum nickel content should not exceed 65 percent since it is essential that the alloy include sufiicient amounts of the other elements to insure that it has the requisite properties.

An alloy having the above mentioned elements in the indicated ranges has good high temperature strength and thermal stability as well as good resistance to corrosion, oxidation and wear. Furthermore, the alloy can be satisfactorily hot worked and machined. As stated above, the known materials designed for high temperature engine use only partially meet these requirements and, hence, design restrictions have been imposed by the various limitations.

In order to determine effects of chemistry variations on the properties of our alloy, :1 number of test heats were melted. The composition of the various test heats is set forth in Table I.

TABLE I Composition (Percent) L 4317 L 4318 L 4319 L 4320 L 4321 L 4322 L 4586 C 0.38 0. 40 0. 42 0.37 O. 43 0.37 0. 36 M n 0. 20 0.20 0.20 0. 20 0.20 0.20 0. 18 S1 O. 20 0. 20 0. 20 0. 20 0. 20 0. 20 0. 22 Cr 24. 30 24. 36 24. 48 24. 70 24. 52 28. 56 24. 46 7. 27 6.87 7. 09 8.88 7.30 6. 69 *2. *2. 0 *2. 0 *2. 0 *2. 0 1. 82 10. 04 10 08 10.24 9. 99 J. 92 9. 74

*Maximum iron content.

Tests were carried out on the various alloys and the results of these tests are set forth in Tables II and III. The test results demonstrate the desirable properties of alloys having a composition within our ranges. The product of each heat was cast into two 2 ingots and each ingot was longitudinally ground prior to fabrication. The ingots are identified hereinafter by the heat number followed by a l or a 2. The ingots from each heat were hot worked in the manner indicated in Table II at 2250 F. and the results of the working are shown.

TABLE II Heat Method of Working workability L 4317l Roll Unsatisfactory.

Forge and roll. Do. 1 Do. Forge and roll. Do.

Forge and r0 o.

Unsatisfactory. Forge and roll Do.

Very unsatisfactory. Forge and roll Do. D0. Forge and roll. Do.

o Satisfactory 1586-2 .do Do.

A consideration of the above data in Table It indicates that alloys containing molybdenum and nitrogen could not be successfully hot worked. The product of each heat to which molybdenum was added and of the heat to which nitrogen was added could not be satisfactorily worked. Additionally, the workability was adversely affected by excessive amounts of chromium and tungsten as is indicated by the very unsatisfactory hot workability rating for the products of heats L 4321 and L 4322. The Workability of the product of these two heats was poorer than;- the workability of heat L 4317 although all three heats contained approximately the same amount of molybdenum.

As a result of the general poor workability of the rolled bar product, it was only possible to carry out further tests on the rolled products from three heats. Creep tests were conducted on specimens from heats L 4317, L 4319 and L 4586 and the results of the tests are set forth in Table III. In each instance the test specimens were treated by heating to 2150 F. for two hours, followed by air cooling, followed by heating to 1400" F. for sixteen hours, followed by air cooling. Each test was carried out at 1350 F. at a stress of 20,000 p.s.i.

TABLE III Heat: Time to 1.0% creep (hours) L 43171 114.8 L 43l9-2 224.5 L 43192 309.0 L 45862 412.5 L 45862 402.0

The data set forth in Table III shows that alloys having a composition within the ranges of the present invention exhibit excellent strength properties as shown by the time to 1% elongation. It is significant to note that the four specimens from the heats having an analysis within the ranges of the invention required a minimum of about twice the time for 1% elongation than that required for heat L 43171 which included molybdenum.

A commercial size heat was also melted and the product obtained was worked and tested. The heat was melted in a vacuum induction furnace and the resulting product had the following composition:

Percent C 0.42 Mn 0.02

The product was cast into one 10" square ingot and one 9%" round ingot. The 9%" ingot was then remelted in a consumable electrode electric furnace, and the heat was cast into a 13" round ingot. The resulting 13" ingot was then satisfactorily hot worked to 9" square by press forging at conventional temperatures for hot working high alloy steels.

The ingot cast from the commercial size heat was press forged to 6" square after which it was ground. Subsequent to grinding, the ingot was reheated and again press forged to 4 /2" square. The 4 /2" square was reheated and hot rolled to a 2" round bar. The satisfactory working of the 10" ingot into 2" bar confirmed the conclusions as to workability shown by the results of the test heats.

Creep tests were conducted on two specimens cut from the 2" bar at a temperature of 1350 F. and a stress of 20,000 psi. The test specimens were maintained under these conditions for 100 hours after which time they showed elongations of 0.36% and 0.37%. The amount of elongation obtained in 100 hours shows that it would take in excess of 300 hours to reach 1% elongation at this temperature and stress, and the results of the creep tests therefore agree with the results of similar tests carried out on test specimens.

Thus, the workability and creep strength obtained on the product of a commercial size heat agree with the results obtained on the test heats and are considerably better than these properties in known materials.

It is readily apparent from the foregoing test data that the alloy of the present invention exhibits good high temperature strength and stability and can be satisfactorily worked and machined.

The invention may be embodied within the scope of the appended claims.

We claim:

1. A high temperature nickel base alloy consisting essentially of carbon from 0.20 to 0.60%, manganese up to 0.30% max., silicon up to 0.35% max., chromium from 22.5 to 24.5%, tungsten from 5.0 to 8.0%, cobalt from 5.0 to 12.0%, iron up to 3.0% max., balance nickel, said nickel being present in an amount of from 50.0 to 65.0%, said alloy being characterized by good high temperature strength, good thermal stability, good resistance to corrosion, oxidation and wear, satisfactory workability and machineability.

2. A high temperature nickel base alloy consisting essentially of carbon from 0.35 to 0.45 manganese up to 0.30% max., silicon up to 0.35% max., chromium from 22.5 to 24.5%, tungsten from 6.0 to 8.0%, cobalt from 8.0 to 10.25%, iron up to 3.0% max., balance nickel, said nickel being present in an amount of from 50.0 to 65.0%, said alloy being characterized by good high temperature strength, good thermal stability, good resistance to corrosion, oxidation and wear, satisfactory workability and machineability.

3. A high temperature nickel base alloy consisting essentially of about 0.40% carbon, about 0.20% manganese, about 0.20% silicon, about 24.0% chromium, about 7.0% tungsten, about 10.0% cobalt, up to about 2.0% iron and the balance substantially all nickel and incidental impurities, said alloy being characterized by good high temperature strength, good thermal stability, good resistance to corrosion, oxidation and wear, and satisfactory workability and machineability.

4. A nickel base alloy engine part having good oxidation and corrosion resistance, good resistance to creep and satisfactory fabricability, said part consisting essentially of carbon from 0.20 to 0.60%, manganese up to 0.30% max., silicon up to 0.35% max., chromium from 22.5 to 24.5%, tungsten from 5.0 to 8.0%, cobalt from 5.0 to 12.0%, iron up to 3.0% max., balance nickel, said nickel being present in an amount of from to said part being heat treated by heating to 2150 F. for 16 hours, followed by air cooling.

5. A nickel base alloy engine part having good oxidation and corrosion resistance, good resistance to creep and satisfactory fabricability, said part consisting essentially of carbon from 0.35 to 0.45%, manganese up to 0.30% max., silicion up to 0.35% max., chromium from 22.5 to 24.5%, tungsten from 6.0 to 8.0%, cobalt from 8.0 to 10.25%, iron up to 3.0% max., balance nickel, said nickel being present in an amount of from 50 to 65%, said part being heat treated by heating to 2150 F. for two hours, followed by air cooling and then heating to 1400 F. for 16 hours, followed by air cooling.

References Cited UNITED STATES PATENTS 9/1950 Great Britain.

CHARLES N. LOVELL, Primary Examiner.

Patent No. 3,393,999

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION July 23, 1968 Louis W. Lherbier et a1.

It is certified that error appears in the above identified patent and that said Letters Patent are hereby corrected as show below:

Column 4, TABLE II, first column, line 8 thereof, "L 4329-2" should read L 4320-2 Column 6 line 30 "silicion" should read silicon Signed and sealed this 23rd day of December 1969.

(SEAL) Attest:

Edward M. Fletcher, Jr.

Attesting Officer Commissioner of Patents WILLIAM E. SCHUYLER, JR. 

